1. Field of the Invention
The invention relates to a device for forming a leno selvedge with an electric motor comprising a rotor and a stator accommodating the rotor, whereas the rotor is provided with at least two guiding apertures for the doup ends and whereas the rotor is provided with several magnetic poles oriented in axial direction.
2. Description of the Prior Art
The document EP 674 031 discloses a so-called rotary selvedge twisting apparatus for power-operated looms provided with a ring serving as a rotor and lodged in a casing designed as a stator. This ring, which may also be called a disc, has two guiding apertures for threading the doup ends. According to the state of the art, the ring is additionally provided radially, i.e. on its outer periphery, with magnets arranged thereon and cooperating with the corresponding laminations arranged in the stator casing. As the rotor revolves in the casing, the doup ends guided by the rotor in the two thread guiding apertures are twisted, whereas at each twist one weft thread is firmly locked in place by this twisting. The principle of operation of such a device for forming a leno selvedge is sufficiently well known.
This well-known device for forming a leno selvedge, which, as already described above, is designed as an electric motor, the magnets for the electric motor being tangentially arranged on the periphery of the rotor and the stator being accordingly provided with corresponding laminations, is characterized by a reduced speed and a high moment of inertia. This is a disadvantage since, when using this contrivance as a device for forming a full leno selvedge, the direction of rotation of the rotor must be reversed after a determined number of revolutions in order to undo a twisting of the doup ends on the feeding side of the doup ends. Since the time available for such an inversion of the direction of rotation is very short due to the high number of weft on modern power-operated looms, the motor must have an extremely high velocity while having a small moment of inertia.
A rotary selvedge twisting apparatus of the type mentioned above is described in DE 297 13723.9, said twisting apparatus being provided with a stator and a doup disc, the doup disc having on its one side magnets oriented toward the stator. These magnets are arranged on the actual disc body. The short circuit obviously occurs on one side of the disc, namely on the side facing the stator.
The disadvantage thereof is that the power density that may be achieved with this well-known structural shape of a rotary selvedge twisting apparatus is small.
U.S. Pat. No. 4,330,737 describes the rotor as being accommodated by the stator casing in axial direction on both sides, the stator casing being provided with iron cores with appropriate windings. The ends of the windings are pointing toward each other, though. As a result, the motor cannot have the required dynamics and power that would be necessary to utilize it in a device for forming a leno selvedge since the magnetic flux is not optimal.
U.S. Pat. No. 3,700,942 discloses a motor in which the rotor is locked on both sides by the stator casing. The rotor is also provided with magnetic poles but it has to be noted that the coil of the stator casing is arranged on the front relative to the rotor in the stator casing. This signifies that, in principle just as in the embodiment according to DE 297 13 723, the magnetic field lines form a leakage flux on account of the air gap to be overcome, which brings about a considerable decrease of performance.